sparse .* rowvec is dense

[JeffBezanson]

but sparse .* vec gives sparse:

julia> m = sprand(5,5,.2)
5×5 SparseMatrixCSC{Float64,Int64} with 4 stored entries:
  [1, 1]  =  0.553674
  [3, 1]  =  0.431147
  [5, 1]  =  0.324723
  [1, 3]  =  0.248959

julia> v = rand(5);

julia> m .* v'
5×5 Array{Float64,2}:
 0.419685  0.0  0.178785  0.0  0.0
 0.0       0.0  0.0       0.0  0.0
 0.32681   0.0  0.0       0.0  0.0
 0.0       0.0  0.0       0.0  0.0
 0.24614   0.0  0.0       0.0  0.0

julia> m .* v
5×5 SparseMatrixCSC{Float64,Int64} with 4 stored entries:
  [1, 1]  =  0.419685
  [3, 1]  =  0.309619
  [5, 1]  =  0.261807
  [1, 3]  =  0.188711

In 0.5 they both give sparse.

[pabloferz]

#20102 should fix this, but it needs more discussion. I could take out the bits that would solve this issue and submit a separate PR though (by could I mean will).